The immediate-type hypersensitivity, such as extrinsic asthma, hay fever, and allergic responses to certain food or drugs, is mediated primarily by immunoglobulin E (IgE). In an IgE-mediated allergic response, the allergen binds to IgE on the surface of mast cells and basophilic leukocytes (basophils). This binding causes a crosslinking of the IgE molecules and hence the underlying receptors for the Fc portion of IgE (Fc.epsilon.R) and thereby triggers the release of pharmacologic mediators such as histamine, slow-reacting substance of anaphylaxis and serotonin. The release of these mast cell and basophil products causes the various pathological manifestations of allergy.
Patients affected with IgE-mediated hypersensitivities reactions are often treated with histamine antagonists to alleviate symptoms. In addition, during hay fever seasons, desensitization procedures are used to prevent or to alleviate persistent, lasting allergic reactions. In these procedures, small doses of allergen are injected periodically to induce certain, not-fully-understood immune responses that somehow reduce the IgE-mediated responses. Densensitization procedures have been effective in certain patients and only marginally effective in others.
It has been suggested that IgE-mediated allergy might be treated by inhibiting the binding of IgE to mast cells and basophils. For example, synthetic peptides representing various regions of the Fc of IgE (Fc.epsilon.) have been explored as competitive inhibitors for the binding of IgE to the receptors on mast cells and basophils. See e.g., Stanworth, D. R., Molec. Immun. 21:1183-1190 (1984); Stanworth, D. R. and Burt, D. S., Molec. Immun. 23:1231-1235 (1986); Burt, D. S. et al., Molec. Immun. 24:379-389 (1987); Hahn, U.S. Pat. No. 4,683,292; Hamburger, U.S. Pat. Nos. 4,171,299 and 4,161,522. However, presumably due to the much lower affinity of these peptides compared with whole IgE for the Fc.epsilon.R, such peptides have not been proven highly efficacious for treatment of allergy.
In recent years, monoclonal antibody methodologies have been employed to map the various antigen and functional epitopes on IgE. Baniyash and Eshhar (Eur. J. Immunol. 14:799-807 (1984)) reported that among the several rat monoclonal antibodies made against IgE, three inhibited the binding of mouse IgE to rat basophils cells. Since the antibodies could also induce serotonin release from basophils bound with IgE, the antibodies probably bound sites on Fc, which were near but not in the site binding to the receptors for IgE on basophils. Hook et al. also published a number of abstracts (see Fed. Proc. 40:965 (1981), Fed. Proc. 46:1346 (1987)) reporting that among approximately ten mouse monoclonal antibodies made against human IgE, a few could not bind IgE on basophils. These studies have addressed to the use of monoclonal antibodies to define the various epitopes or functionally related peptidic segments on IgE.
Recently, Whitaker described an immunotoxin specific for the IgE isotype and its use in the treatment of allergy. U.S. Pat. No. 4,714,759. The immunotoxin comprises an anti-IgE antibody coupled to a toxin. The intended pharmacologic mechanism of the treatment is that the immunotoxin specific for IgE isotype would kill IgE-producing B cells.